A study of the prevalence of early onset periodontitis in U.S. children aged 14 to 17 years has been completed and was published in October, 1991. In a national survey, the total number of adolescents affected by LJP was about 70,000. Seventeen thousand were estimated to have GJP and another 212,000 adolescents had incidental LA (r3mm on 1 or more teeth). Blacks were at greater risk of all forms of early onset periodontitis than whites. Males were more likely (4.3 to 1) to have GJP than females when other variables were statistically controlled. A major contract to relocate, re-examine and collect risk factor information on these children began in October, 1991. Research objectives are to: a) assess the progression of periodontal destruction among the cases of early onset periodontitis, b) characterize the microbial ecology of the sub-gingival plaque among persons with early onset periodontitis, c) describe periodontal destruction and the presence of biologic and non-biologic putative risk markers among the probands' similar aged siblings, and d) compare the presence and concentration of selected putative pathogens and high-resistance factors among individuals with early onset periodontitis to controls.